Two Years With Linux BFS, The Brain Fuck Scheduler

This month marks the two-year anniversary of the release of BFS,
the Brain Fuck Scheduler, for the Linux kernel. While BFS has not been merged
into the mainline Linux kernel, the scheduler is still actively maintained by
Con Kolivas and patches are updated for new kernel releases. The BFS scheduler
has also reached mild success and adoption over the past two years. In this article
is a fresh look at the Brain Fuck Scheduler along with a fresh round of benchmarks
from the Linux
3.0 kernel.

When Con Kolivas announced the Brain Fuck Scheduler (BFS) as an
alternative to the Completely Fair Scheduler (CFS) that is the default scheduler
in the mainline Linux kernel, he expressed straight away that he was not aiming
this patch for inclusion into the mainline kernel tree. BFS takes a much simpler
design approach than CFS, which was written by Ingo Molnar and originally inspired
by the CPU scheduling work of Con Kolivas years before he conceived the new scheduler.
The reasoning is that Kolivas is not motivated to push it upstream and that the
Brain Fuck Scheduler is designed to improve the CPU scheduling experience for
desktops and systems with few-cores-or-less. BFS is not written to scale to systems
with many processing cores, thus not making it ideal for powerful servers and
workstations, and not a one-all replacement for CFS. There is also no interest
in the Linux kernel development community of having multiple schedulers available
in the mainline tree.

While BFS is not in the mainline Linux kernel tree, a few Linux
distributions ship with a kernel that is patched for the Brain Fuck Scheduler.
Among the BFS-enabled distributions are Zenwalk, PC Linux OS, and Kanotix. There
is also a branch of Google's Android operating system that has BFS support, since
mobile devices fit the light-NUMA target of the low-overhead scheduler well. In
addition, a steady stream of Linux users are manually patching the Brain Fuck
Scheduler for their own kernel on other distributions.

Kolivas continues to update his BFS scheduler patch for every
major Linux kernel release since Linux 2.6.31 and are available from his Kolivas.org
server. The most recent patch by Con Kolivas is from 11 August and for the
Linux 3.0 scheduler with BFS v0.406, which is what is being tested in this article.
For those interested in more technical details about the Brain Fuck Scheduler,
Kolivas continues to maintain the
BFS FAQ page.

Shortly after the release of BFS in 2009, there were Phoronix
benchmarks of the BFS scheduler,
which showed mixed results. There have not been benchmarks since then of this
new scheduler, which should make today's results particularly interesting. In
this article we're using an Intel "Sandy Bridge" system while benchmarking
the latest BFS (v0.406) patch on the Linux 3.0 kernel and comparing it to the
Completely Fair Scheduler as used by default in the kernel tree. Besides swapping
the scheduler, this was a vanilla Linux 3.0 kernel build using an otherwise stock
kernel configuration.

The BFS mascot? Found on a wall in Berlin Mitte...

The Sandy Bridge system had an Intel Core i5 2500K CPU, Sapphire
Pure Black P67 Hydra motherboard, 4GB of RAM, 64GB OCZ Agility SSD, and a NVIDIA
GeForce GTX 460 graphics card. The software stack was 64-bit Ubuntu 11.04, the
GNOME 2.32.1 desktop, X.Org Server 1.10.1, GCC 4.5.2, and an EXT4 file-system.
Making these Brain Fuck Scheduler results even more interesting is that this physical
quad-core Core i5 CPU was tested with BFS and CFS when one, two, and four cores
were enabled from the BIOS.

Benchmarking was done via the Phoronix
Test Suite automated open-source testing infrastructure. Beyond running a
variety of CPU-focused tests, the CPU usage while running several of the tests
was also looked at to further compare the Brain Fuck Scheduler and Completely
Fair Scheduler.